U.S. Fish and Wildlife Service
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Life History

Mucket - Actinonaias ligamentina

Butterfly  - Ellipsaria lineolata

Plain pocketbook - Lampsilis cardium
Plain pocketbook

Giant floater - Pyganodon (=Anodonta) grandis
Giant floater

Fragile papershell - Leptodea fragilis
Fragile papershell

Threeridge - Amblema plicata

Mapleleaf  - Quadrula quadrula

Higgins' eye - Lampsilis higginsii
Higgins' eye

Fatmucket - Lampsilis siliquoidea

Yellow sandshell - Lampsilis teres anondontoides
Yellow sandshell

Black sandshell - Ligumia recta
Black sandshell

Pondmussel - Ligumia subrostrata

Threehorn wartyback - Obliquaria reflexa
Threehorn wartyback

Hickorynut - Obovaria olivaria

Pink heelsplitter - Potamilus alatus
Pink heelsplitter

Fat pocketbook - Potamilus capax
Fat pocketbook

Pink papershell - Potamilus ohiensis
Pink papershell

Bleufer - Potamilus purpuratus

Lilliput - Toxolasma parvus

Fawnsfoot - Truncilla donaciformis

Deertoe - Truncilla truncata Deertoe

Pistolgrip - Tritogonia verrucosa

Elktoe - Alasmidonta marginata

Flat floater - Anodonta suborbiculata
Flat floater

Rock pocketbook - Arcidens confragosus
Rock pocketbook

White heelsplitter - Lasmigona c. complanata
White heelsplitter

Purple wartyback - Cyclonaias tuberculata
Purple wartyback

Ebonyshell - Fusconaia ebena

Elephantear - Elliptio crassidens

Creeper - Strophitus undulatus

Paper pondshell - Utterbackia (=Anodonta) imbecillis
Paper pondshell
Mucket - Actinonaias ligamentina

Butterfly  - Ellipsaria lineolata

A mussel is a relatively simple animal enclosed by two shells connected by a ligament. The shells are formed largely out of calcium carbonate that has been extracted from the waters where mussels live. The calcium carbonate is then deposited in successive layers. The hard shell provides some protection for the inner animal. Internally, the body consists of gills for breathing, a digestive tract for processing food, a large muscular foot for locomotion, and mantle tissue that produces the shell.

Freshwater mussels are extremely variable with respect to life span, coloration, and size. For example, some species live for only 10 years and others may live for as long as 100 years.

Mussel anatomy
mussel anatomy (.gif) Click for larger scale.
Click for larger scale

Shell color can range from yellow to green to brown to black and may contain bumps, tubercles, and ridges or can remain very smooth. Species range in size from only one inch to over one foot. Thin-shelled species like the giant floater and fragile papershell grow much faster than thicker-shelled species like the threeridge and mapleleaf. Mussels have very colorful common names such as monkeyface, threehorn wartyback, rough pigtoe, spike, and pink heelsplitter.

Life Cycle of a Mussel
Click for larger scale

Freshwater mussels have a unique life cycle. Unlike oysters and clams, most freshwater mussels need a fish to complete their life cycle. Some mussels require a specific host fish to complete their life cycle; others can use a variety of fish species. For more information on host fish, click here. In the wild, male mussels release sperm into the water column. The sperm are drawn into the female as she filters water for food. The fertilized eggs reside within pouches (marsupia) of the modified gills and develop into larvae termed glochidia--tiny creatures that are parasitic and must find a suitable fish host to complete their life cycle.

Glochidia are triangular, spherical, or hatch-shaped and range in diameter from 0.08 to 0.35 millimeters. A single female can carry from a few thousand to several million glochidia.

Glochidia of the Higgins' eye pearlymussel
Lampsilis higginsii
Lampsilis higginsii glochidia
click for larger scale

To help them find a host fish, some species have modified their mantle tissue (the tissue that lines the inside of the shell) so that it looks like a minnow.

Fish lure of the Broken-rays mussel - Lampsilis reeveiana
Broken-rays mussel - Lampsilis reeveiana
Click for larger scale

The female Higgins' eye pearlymussel can undulate this minnow-like structure so that this “lure” attracts fish looking for food. When a fish bites the lure, the female releases the glochidia from her gills and the glochidia attach to the gills or fins of the fish.

Fish lure of the Higgins' eye pearlymussel - Lampsilis higginsii

Click for larger scale

Click for larger scale

Other species release their glochidia in a special package resembling an insect larvae or small fish. Each package contains thousands of glochidia. When the host fish bites the “fake” insect larvae or fish, it ruptures and spills its contents of glochidia into the fish’s mouth. Click here to see other mussel displays and lures.

Glochidia package (ovisac) of the Ouachita kidneyshell mussel
Ptychobranchus occidentalis

Click for larger scale

Click for larger image

Depending on the species, glochidia remain attached to the host fish for about 3 days to 10 months (depending primarily on water temperature) while transforming into juvenile mussels.

Transformation of glochidia from Higgins' eye pearlymussels
Higgins' eye glochidia
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glochidia on fish gills
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glochidia on encyst
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juvenile and pinhead
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Glochidia (top left) attach to the gills of host fish (top right) and encyst (bottom left). In approximately 3 weeks they transform, fall off the gills and settle to the bottom as juveniles. The juvenile is approximately 0.75 millimieters long; it is shown next to the head of a pin (bottom right) for size comparison.

Glochidia do not appear to harm the host fish and when the transformation is complete, they drop off the fish, land on the bottom of the river, and begin their life as a free living organism. The bottom line is that glochidia must attach to the correct host fish in order for it to complete its life cycle.

Examples of this intricate dependence of mussels on fish are the ebony shell and elephantear mussels. Both species rely on the skipjack herring as their sole fish host.

The construction of Lock and Dam 19 on the Upper Mississippi River at Keokuk, Iowa, blocked the upstream migration of skipjack herring. As a result, these two mussels are no longer found upstream of Lock and Dam 19.

Lock and Dam 19 on the Upper Mississippi River at Keokuk, Iowa
Upper Mississippi River Lock and Dam 19
Source: Keokuk Office of Tourism

Species Identification and LocationThreatened and Endangered MusselsLife HistoryEcology Mussel Harvest on the RiverCurrent ThreatsMussel Conservation ActivitiesOngoing Studies and ProjectsMultimediaTeacher ResourcesFrequently Asked QuestionsGlossaryReferencesLinks to Other Mussel Sites


Department of the InteriorU.S. Fish & Wildlife ServiceU.S. Geological Survey
Last updated on December 18, 2006